In commercial buildings electrical peaks, or predetermined electrical load limits, are usually set on hot days due to large air conditioning requirements. Electrical demand limiting can save significant money if an effective way of dealing with the peak demand of air conditioning can be accomplished. One way to deal with the problem is by selectively raising zone thermostat setpoints to shed electrical load when demand approaches a perdetermined limit. This has been done previously by actually raising the setpoint of each thermostat which controls a zone temperature. The technique of raising the thermostat setpoint during demand periods is somewhat effective, but also has some drawbacks.
To be effective, the load should be somewhat responsive such that when high demand occurs, shedding the load will provide immediate electrical reduction. When the demand drops, the load should be brought back to normal so that the load can be shed again for load reduction at the occurance of a subsequent peak. After a thermostat setpoint has been raised, it requires a slow recovery to the normal setpoint to avoid bringing on too many cooling stages simultaneously, and thereby causing another peak demand situation. This mean that the scheme of raising a setpoint is not very dynamic since a setpoint can not successfully recover for approximately forty five minutes to one hour after the setpoint has been raised. This scheme will not make the most efficient use of the controlled loads for limiting the electrical demand in a building.